You need to have a Apple Music Family Membership to be able to share it with other members of your Family Group. You cannot share an Individual membership.
To use a Family Membership with other people in your family, set up Family Sharing using a supported device. When you set up Family Sharing, you become the family organizer. If you don't want to be the family organizer, ask someone else to set up Family Sharing.
If you've already set up Family Sharing and joined Apple Music with a Family Membership, you can add new people to your Family Membership by inviting them to be a part of your family group.